为什么在RTT里读取一次CNT寄存器的值就会少一个脉冲呢

用的定时器3的通道检测外部脉冲个数，每隔一秒读取一次CNT寄存器的值，标准库下脉冲数量正常，但是RTT里读取就会少一个脉冲



上面打印的是标准库，下面打印的是RTT
RTT NANO 使用定时器ETR外部计数时会丢失脉冲

定时器代码：定时器3外部计数，定时器2产生脉冲


#include "led.h"
#include "rtthread.h"
static int LED_Init(void)
{
    GPIO_InitTypeDef  GPIO_InitStructure;
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOD, ENABLE);   
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;               
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;         
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;        
    GPIO_Init(GPIOD, &GPIO_InitStructure);                     
    GPIO_SetBits(GPIOD,GPIO_Pin_2);     
    return 0;
}
INIT_BOARD_EXPORT(LED_Init);
static int bsp_timer3_init(void)
{
    TIM_TimeBaseInitTypeDef      TIM_TimeBaseStructure;
    GPIO_InitTypeDef              GPIO_InitStructure;
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
    TIM_TimeBaseStructure.TIM_Period = 65535;
    TIM_TimeBaseStructure.TIM_Prescaler = 0;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
    TIM_TIxExternalClockConfig(TIM3,TIM_TIxExternalCLK1Source_TI1,TIM_ICPolarity_Rising,0);
    TIM_SetCounter(TIM3, 0);
    TIM_Cmd(TIM3, ENABLE);
    return 0;
}
INIT_BOARD_EXPORT(bsp_timer3_init);
static int  bsp_timer2_init(void)
{
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    NVIC_InitTypeDef NVIC_InitStructure;
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    TIM_TimeBaseStructure.TIM_Period = 100-1;
    TIM_TimeBaseStructure.TIM_Prescaler = 72-1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE );
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
    TIM_SetCounter( TIM2, 0 );
    TIM_Cmd(TIM2, ENABLE);
    return 0;
}
INIT_BOARD_EXPORT(bsp_timer2_init);
void TIM2_IRQHandler(void)
{
    if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)
    {
        LED1=!LED1;
        LED1=!LED1;
    }
    TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
}
主函数：
rt_thread_t USART_tid;
static void USART_thread_entry(void* params)
{
    while(1)
    {
        rt_kprintf("Count=%d
",TIM_GetCounter(TIM3));
        TIM_SetCounter(TIM3, 0);
        rt_thread_mdelay(1000);
    }
}
int USART_thread(void)
{
    USART_tid = rt_thread_create("USART", USART_thread_entry, RT_NULL, 256, 10, 5);
    if(USART_tid != RT_NULL)
        rt_thread_startup(USART_tid);
    return 0;
}
int main(void)
{   
    USART_thread();
}